Sputtering, alternatively called physical vapor deposition (PVD), has long been used in depositing metals and related materials in the fabrication of semiconductor integrated circuits. Its use has been extended to depositing metal layers onto the sidewalls of high aspect-ratio holes such as vias or other vertical interconnect structures. Currently, advanced sputtering applications include depositing a metallic seed layer for later electroplating of the metallic layer in the via and depositing a barrier layer on the dielectric material of the via sidewall to prevent the metallic layer from diffusing into the dielectric.
Plasma sputtering may be accomplished using either DC sputtering or RF sputtering. Plasma sputtering typically includes a magnetron positioned at the back of the sputtering target to project a magnetic field into the processing space to increase the density of the plasma and enhance the sputtering rate. Magnets used in the magnetron are typically closed loop for DC sputtering and open loop for RF sputtering. DC plasmas closely confine the electrons into a closed loop race track or else the target voltage becomes very high and does not support sputtering at reasonable voltage and pressure. RF sputtering is very flexible and can work with almost any magnetic field, but if the field is too high, then the plasma can over-concentrate in the race track area. Any over concentration of the RF plasma can lead to very low target voltages and very low sputter rates. However, typical magnetrons do not provide both open loop and closed loop PVD magnets to be selectively used based on the type of sputtering required (i.e., DC or RF sputtering).
Thus, the inventors have provided a magnet configuration that can advantageously provide both DC and RF plasma confinement in the same chamber with the same hardware.